Evaluation of bone stimulation by different designs of microthreaded implants in enhancing osseointegration: An in vivo animal study supported by a numerical analysis

Optimization of stress distribution of bone-implant interface (BII)

Many studies have found that the threshold of occlusal force tolerated by titanium-based implants is significantly lower than that of natural teeth due to differences in biomechanical mechanisms. Therefore, implants are considered to be susceptible to occlusal trauma. In clinical practice, many implants have shown satisfactory biocompatibility, but the balance between biomechanics and biofunction remains a huge clinical challenge. This paper comprehensively analyzes and summarizes various stress distribution optimization methods to explore strategies for improving the resistance of the implants to adverse stress. Improving stress resistance reduces occlusal trauma and shortens the gap between implants and natural teeth in occlusal function. The study found that: 1) specific implant-abutment connection design can change the force transfer efficiency and force conduction direction of the load at the BII; 2) reasonable implant surface structure and morphological character design can promote osseointegration, maintain alveolar bone height, and reduce the maximum effective stress at the BII; and 3) the elastic modulus of implants matched to surrounding bone tissue can reduce the stress shielding, resulting in a more uniform stress distribution at the BII. This study concluded that the core BII stress distribution optimization lies in increasing the stress distribution area and reducing the local stress peak value at the BII. This improves the biomechanical adaptability of the implants, increasing their long-term survival rate.

Probability of survival and stress distribution of narrow diameter implants with different implant-abutment taper angles

This study evaluated the probability of survival, failure mode, and stress distribution of narrow diameter implants (NDIs) with internal implant-abutment conical connection comprised of different taper angles and thread designs. Sixty-three NDIs (Ø 3.5 × 8.5 mm) were divided according to the taper angle (TA), internal diameter (ID), and trapezoidal thread design (TD) (n = 21/group), as follows: (a) 11.5°U (11.5° TA; ID: 2.5 mm; TD: dual threaded); (b) 11.5°S (11.5° TA; ID: 2.5 mm; TD: single threaded); (c) 16°S (16° TA; ID: 2.72 mm; TD: single threaded). They were subjected to step-stress accelerated life testing. The reliability and use-level probability Weibull curves were calculated at 50, 100, and 150 N for a mission of 100,000 cycles and the failure mode was analyzed using a scanning electron microscope. For finite element analysis the von-Mises stress (σ_vM ) was calculated for the abutment and implant. All groups showed high reliability (above 84%) and failures occurred predominantly in the abutment. In the FEA, 11.5°U showed higher σ_vM for the implant. All NDIs showed high reliability at clinically challenging loads. The system with greater taper angle showed lower σ_Vm in the implant, and dual threaded implants showed a higher stress concentration in the implant and cortical bone.

Evaluation of hydrophilic gel made from Acemannan and Moringa oleifera in enhancing osseointegration of dental implants. A preliminary study in rabbits

BACKGROUND

Hydrophilic implant surface has gained increasing interest as a factor to stimulate osseointegration.

PURPOSE

The study was done to formulate hydrophilic gel to be applied on to the dental implant surface, to enhance bone to implant contact (BIC).

MATERIALS AND METHODS

In first part of study, Acemannan and Moringa oleifera hydro gel formulated in different proportions were coated on the titanium disk and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT) assay was done to evaluate cell viability.Cytotoxicity of aqueous extracts of two plants were tested against UMR106 cells. In second part of study, the prototype titanium implants were placed in tibia and femur of 8 male rabbits. Hydrophilic gel formulated from Acemannan and Moringa oleifera were coated on the study groups of implants. Histomorphometric analysis was carried out of the enbloc sections specimens. Student's unpaired t-test was used to compare mean values between the two groups.

RESULTS

The alkaline phosphatase assay showed least cell inhibition for Acemannan and Moringa oleifera (2:1) as 4.45% and osteoblastic differentiation as 0.328 at 540 nm. Titamium disc coated with hydrogel of Acemannan and Moringa oliefera and seeded with Human MSC shows increased proliferation of osteoblast cells.Compare to study group implants, control group showed no new bone formation.

CONCLUSIONS

Hydrophilic implant surface showed new bone formation with increased bone to implant contact.There was absent of degenerative changes, necrotic changes, fibrosis, and inflammation at the new BIC.

Bone Marrow Mesenchymal Stromal Cells (BMMSCs) Augment Osteointegration of Dental Implants in Type 1 Diabetic Rabbits: An X-Ray Micro-Computed Tomographic Evaluation

Background and objectives: The study aimed to investigate the effect of bone marrow mesenchymal stromal cells (BMMSCs) on implant-bone osseointegration in type I diabetic New Zealand rabbits. Materials and methods: BMMSCs harvested from healthy rabbits were processed and validated for purity and osteocyte differentiability. Mandibular incisors of diabetic and control rabbits were carefully extracted, and the sockets were plugged with collagen sponges. Platelet-rich plasma (PRP) containing osteoinductive BMMSCs, and plain PRP were injected into the collagen sponge of the right and left sockets respectively. Dental implants of 2.6 mm diameter and 10 mm length were inserted into the collagen sponge of both sockets. All the animals were sacrificed six weeks post surgery to evaluate an early stage of osseointegration; the mandibles scanned by X-ray microcomputed tomography (μCT) and subjected to 3D analysis. The μCT parameters of the right implant were paired against that of the left side of each animal and analyzed by paired T-test. Results: The preclinical evaluation of the viability and osteocyte differentiation of the BMMSCs were consistent between both the donor samples. The osseointegration of dental implants with stem cell therapy (BMMSCs + PRP + collagen) in normal and diabetic rabbits was significantly higher than that of implants with adjunctive PRP + collagen only (p < 0.05). Conclusion: Stem Cell therapy with osteoinductive BMMSCs and PRP can offer a novel approach to enhance the osseointegration of dental implants in uncontrolled diabetic patients.

Effects of occlusal forces on the peri-implant-bone interface stability

The occlusal forces and their influence on the initiation of peri-implant bone loss or their relationship with peri-implantitis have created discussion during the past 30 years given the discrepancies observed in clinical, animal, and finite element analysis studies. Beyond these contradictions, in the case of an osseointegrated implant, the occlusal forces can influence the implant-bone interface and the cells responsible for the bone remodeling in different ways that may result in the maintenance or loss of the osseointegration. This comprehensive review focuses on the information available about the forces transmitted through the implant-crown system to the implant-bone interface and the mechano-transduction phenomena responsible for the bone cells' behavior and their interactions. Knowledge of the basic molecular biology of the peri-implant bone would help clinicians to understand the complex phenomenon of occlusal forces and their effects on the implant-bone interface, and would allow better control of the negative effects of mechanical stresses, leading to therapy with fewer risks and complications.

Statistical analysis of implant and thread parameters effects on dental implant stability and bone resorption using central composite design method

The effect of dental implant parameters, length and diameter, and thread parameters consisting of thread depth, width, pitch and inner angle on Max von-Mises stress in implant–abutment and cancellous bone is investigated. A three-dimensional finite element model of a threaded dental implant and mandibular segment is built. Face-centered central composite design is applied as the design of experiments method to study and optimize the six independent variable parameters at three levels by applying response surface methodology. The simultaneous analysis of these parameters is run to obtain a better perspective on their effects on responses. The effects of linear, square, and interactive terms on responses through Pareto, main effects, and interaction plots are determined through analysis of variance. A second-order polynomial equation is fitted to the model to predict the response magnitude. The results indicate that implant diameter and its interaction with thread depth are effective in decreasing the likelihood of bone resorption. The implant length affects the Max von-Mises stress in implant–abutment, with no effect on the Max von-Mises stress in cancellous bone. The optimization process caused about 10% and 30% reduction in the magnitude of Max von-Mises stress in implant–abutment and cancellous bone, respectively.